The presence of vapors, and their concentration in air, is monitored in many fields of endeavor. Various methods for detecting vapors (e.g., volatile organic compounds (VOCs)) have been developed including, for example, photoionization, gas chromatography, gravimetric techniques, spectroscopic techniques (e.g., mass spectrometry, infrared spectroscopy, or fluorescence spectroscopy), and absorptive sensing techniques.
In capacitance sensors, the capacitance of two conductive electrodes (typically parallel or interdigitated), varies as the dielectric constant of material between the two electrodes changes due to the presence of an environmental analyte vapor. Periodically, it is desirable to remove the analyte from between the conductive electrodes (for example, if switching analyte vapors). In such instances, heating can be used to evaporate the analyte prior to use of the capacitance sensor.